The invention relates to an operating rod for a medical instrument, in particular for an endoscopic instrument which comprises at least two rod parts transmitting tension and/or compression forces and which at their ends facing one another are connected to one another with a positive fit at least in the direction of their longitudinal axis.
Operating rods of this type which for example are applied in endoscopic forceps, transmit tension and compression forces from a handle arranged on the proximal side onto a tool arranged on the distal side, for example the jaw parts of an endoscopic forceps. Due to reasons of hygiene it is often desirable to construct the instrument from several parts so that it can be quickly and simply dismantled for cleaning purposes and later can be put back together again. A multi-part construction is particularly problematic with the operating rod which as a rule is guided within a shank, since the known positive fit connections for this in the form of the usual threaded connections either extends radially projecting or also considerably reduce the effective cross section of the operating rod which is further reduced in practice by the notch effect caused by the fitting of the thread. In particular, with thin operating rods there are at present no known suitable positive fit connections, so that as a rule, one must fall back on material fit connections, that is welding or adhesing. The adhesive connections can be generally neglected since the necessary stability cannot often be guaranteed in particular after repeated sterilization treatment. With welding and soldering connections there then arise problems when materials are used which are not connectable to one another or only with great difficulty, for example stainless steel on the one hand and on the other hand a nickel titanium alloy (memory metal), or for example steel and plastic.
From U.S. Pat. No. 3,220,757 as well as U.S. Pat. No. 5,439,309, positive fit connections of the most general type are known, these being formed by toothed profiles engaging into one another. The positive fit connections disclosed here can also for example be applied to rods, wherein a spring pretensioned cap is provided which secures the toothed profiles in the radial direction with a positive fit. This radial, comparatively bulky cap is not suitable for the connection of slim endoscopic instruments. The positive fit connections described are also quite unstable. Due to the profiled arrangement in the region of the longitudinal center axis, there results a reduction of the effective rod cross section of about one half. Furthermore by way of the toothing arrangement transverse to the longitudinal axis there is a high notch effect. The positive fit connections described are therefore not very suitable for application as an operating rod for an endoscopic instrument.